DNS Problem...

Hi, all! I got a quick question. I am hosting some web pages with users signed up and I make their web page to be like http://usersname.mydomain.com and for some reason sometimes they can hit the web page, and sometimes they can't. I check the message log and I saw some "lame servers on ...." entries. SO is it why?? Is this DNS problem at all? If so, can you pin point me to a solution?

As I said, don't use CNAME, use multiple A record instead. You also have an important A record missing, the ns1.mydomain.com itself. Don't set your MX to mail.mydomain.com, it's extremely unreliable. Set your MX to point to ns1.mydomain.com. Your SOA was incorrect, it should point to ns1.mydomain.com.
It's easily said than done so here comes the example: